Relations between IL-3-induced proliferation and in vitro cytokine secretion of bone marrow cells from AML patients

High CD123 levels enhance proliferation in response to IL-3, but reduce chemotaxis by downregulating CXCR4 expression

High expression of the α chain of the interleukin-3 receptor (IL-3Rα; CD123) is a hallmark of acute myeloid leukemia (AML) leukemic stem cells (LSCs). Elevated CD123 expression is part of the diagnostic immunophenotyping of myeloid leukemia, and higher expression is associated with poor prognosis. However, the biological basis of the poorer prognosis is unclear, and may include heightened IL-3 signaling and non-cell autonomous interactions with the bone marrow (BM) microenvironment. We used TF-1 cells expressing different levels of CD123 and found elevated CD123 levels amplified the proliferative response to exogenous IL-3 and maintained viability in reducing IL-3 concentrations. This was associated with stronger activation of STAT5, Akt, and extracellular signal-regulated kinase 1/2 in vitro. Surprisingly, in vivo e14.5 fetal liver cells transduced with retroviral constructs to express high CD123 failed to engraft in syngeneic recipients. In exploring the underlying mechanism for this, we found that CXCR4, a key molecule involved in LSC/BM interactions, was specifically downregulated in CD123 overexpressing cells in a manner dependent on IL-3 signaling. CXCR4 downregulation was sufficient to alter the chemotactic response of hematopoietic cells to stromal derived factor-1 (SDF-1). Thus, we propose that the overexpression of CD123 in AML LSC dictates their location by altering CXCR4/SDF-1 interaction in the BM, raising the possibility that this mechanism underpins the egress of BM AML LSC and more mature cells into the circulation.

Overexpression of IL-3Rα on CD34+CD38- stem cells defines leukemia-initiating cells in Fanconi anemia AML

Patients with Fanconi anemia (FA) have a high risk of developing acute myeloid leukemia (AML). In this study, we attempted to identify cell-surface markers for leukemia-initiating cells in FA-AML patients. We found that the IL-3 receptor-α (IL-3Rα) is a promising candidate as an leukemia-initiating cell-specific antigen for FA-AML. Whereas IL-3Rα expression is undetectable on normal CD34(+)CD38(-) HSCs, it is overexpressed on CD34(+)CD38(-) cells from FA patients with AML. We examined the leukemia-initiating cell activity of IL-3Rα-positive FA-AML cells in a "humanized" FA xenotransplant model in which we separated AML cells into IL-3Rα-positive and IL-3Rα-negative CD34 fractions and transplanted them into irradiated recipient mice. In all 3 FA-AML samples, only IL-3Rα-positive cells showed significant levels of engraftment and developed leukemia in the recipient mice. The FA CD34(+)IL-3Rα(+) blasts isolated from leukemic mice exhibited hypersensitivity to IL-3 deprivation and JAK2-STAT5 overactivation after IL-3 treatment. Finally, treatment of FA CD34(+)IL-3Rα(+) blasts with an IL-3Rα-neutralizing antibody inhibited IL-3-mediated proliferation and STAT5 activation. These results demonstrate that IL-3Rα is a cell-surface marker present on FA-AML leukemia-initiating cells and may be a valuable therapeutic target.

IL-3 and oncogenic Abl regulate the myeloblast transcriptome by altering mRNA stability

The growth factor interleukin-3 (IL-3) promotes the survival and growth of multipotent hematopoietic progenitors and stimulates myelopoiesis. It has also been reported to oppose terminal granulopoiesis and to support leukemic cell growth through autocrine or paracrine mechanisms. The degree to which IL-3 acts at the posttranscriptional level is largely unknown. We have conducted global mRNA decay profiling and bioinformatic analyses in 32Dcl3 myeloblasts indicating that IL-3 caused immediate early stabilization of hundreds of transcripts in pathways relevant to myeloblast function. Stabilized transcripts were enriched for AU-Response elements (AREs), and an ARE-containing domain from the interleukin-6 (IL-6) 3′-UTR rendered a heterologous gene responsive to IL-3-mediated transcript stabilization. Many IL-3-stabilized transcripts had been associated with leukemic transformation. Deregulated Abl kinase shared with IL-3 the ability to delay turnover of transcripts involved in proliferation or differentiation blockade, relying, in part, on signaling through the Mek/Erk pathway. These findings support a model of IL-3 action through mRNA stability control and suggest that aberrant stabilization of an mRNA network linked to IL-3 contributes to leukemic cell growth.

Monoclonal antibody-mediated targeting of CD123, IL-3 receptor alpha chain, eliminates human acute myeloid leukemic stem cells

Leukemia stem cells (LSCs) initiate and sustain the acute myeloid leukemia (AML) clonal hierarchy and possess biological properties rendering them resistant to conventional chemotherapy. The poor survival of AML patients raises expectations that LSC-targeted therapies might achieve durable remissions. We report that an anti-interleukin-3 (IL-3) receptor alpha chain (CD123)-neutralizing antibody (7G3) targeted AML-LSCs, impairing homing to bone marrow (BM) and activating innate immunity of nonobese diabetic/severe-combined immunodeficient (NOD/SCID) mice. 7G3 treatment profoundly reduced AML-LSC engraftment and improved mouse survival. Mice with pre-established disease showed reduced AML burden in the BM and periphery and impaired secondary transplantation upon treatment, establishing that AML-LSCs were directly targeted. 7G3 inhibited IL-3-mediated intracellular signaling of isolated AML CD34(+)CD38(-) cells in vitro and reduced their survival. These results provide clear validation for therapeutic monoclonal antibody (mAb) targeting of AML-LSCs and for translation of in vivo preclinical research findings toward a clinical application.

Chlamydia pneumoniae induces interleukin-6 and interleukin-10 in human gingival fibroblasts

Chlamydia pneumoniae is an obligate intracellular Gram-negative bacterium with a unique biphasic developmental cycle that can cause persistent infections. In humans, Chlamydia causes airway infection and has been implicated in chronic inflammatory diseases, such as asthma and atherosclerosis. In addition, recent studies demonstrated that patients with severe periodontitis can harbor C. pneumoniae, which can increase the risk for a host inflammatory response with weighty clinical sequelae. Previous studies have established that periodontal pathogenic bacteria (i.e. Gram-negative bacteria) can induce the synthesis and release of cytokines and other inflammatory mediators in human gingival fibroblasts. HGF are resident cells of the periodontium that respond to receptor stimulation by producing a variety of substances including cytokines and growth factors. Our results demonstrate that after 48 hr of incubation with viable C. pneumoniae HGF showed a proliferative response, as seen by both colorimetric MTT assay and direct cell count (30% and 35%, respectively). In addition, HGF incubated with viable or UV light-inactivated C. pneumoniae organisms showed an increase in the levels of IL-6 and IL-10, but not IL-4; on the contrary, HGF infected with heat-killed bacteria did not show a significant production of any of the cytokines considered. In conclusion, the present study suggests that C. pneumoniae may modulate the expression of IL-6 and IL-10 by human gingival fibroblasts. Further studies are warranted to clarify the molecular mechanisms of C. pneumoniae in the regulation of cytokine expression by host cells and to elaborate the relevant clinical implications.

mRNA stability control: a clandestine force in normal and malignant hematopoiesis

This review addresses the scope of influence of mRNA decay on cellular functions and its potential role in normal and malignant hematopoiesis. Evidence is emerging that leukemic oncogenes and hematopoietic cytokines interact with mRNA decay pathways. These pathways can co-regulate functionally related genes through specific motifs in the 3'-untranslated region of targeted transcripts. The steps that link external stimuli to transcript turnover are not fully understood, but include subcellular relocalization or post-transcriptional modification of specific transcript-stabilizing or -destabilizing proteins. Improper functioning of these regulators of mRNA turnover can impede normal cellular differentiation or promote cancers. By delineating how subsets of transcripts decay in synchrony during normal hematopoiesis, it may be possible to determine whether this post-transcriptional regulatory pathway is hijacked in leukemogenesis.

Correlation between expression of CD56/NCAM and severe leukostasis in hyperleukocytic acute myelomonocytic leukaemia

OBJECTIVE

The possible contribution of surface molecules to the development of leukostasis syndrome in hyperleukocytic acute myeloid leukaemia (AML) was assessed by routine immunophenotyping and grading of the probability of clinical leukostasis.

METHODS

Fifty-three patients (23 women, 30 men, median age 59 yr) with hyperleukocytic AML [white blood count (WBC) above 50 x 10(9)/L] were graded for the probability of clinical leukostasis according to the severity of neurologic, pulmonary and other symptoms possibly caused by leukostasis using a recently published scoring system. Age, WBC, absolute blast count, haemoglobin, cytogenetic risk group, infection, relative CD56 expression and absolute count of CD56 positive blasts were analyzed in multivariate stepwise backward logistic regression analysis.

RESULTS

In patients with acute monocytic leukaemia (AML M4/M5) the absolute count of leukaemic blasts expressing CD56/NCAM was highly associated with the development of symptoms graded as highly probable leukostasis and all three patients succumbing to early death were CD56 positive. Only the absolute count of CD56 positive blasts was a significant predictor of risk of severe leukostasis (P = 0.020). This was not found in AML without monocytic involvement (AML M1, M2, M3v).

CONCLUSIONS

The expression of CD56/NCAM, a surface marker used in routine immunophenotyping of AML, may help to predict severe and potentially fatal leukostasis in hyperleukocytic acute myelomonocytic leukaemia. These results emphasize the usefulness of this four-stage clinical grading scale for analysing the factors, which lead to severe leukostasis in hyperleukocytic patients. We extend previous findings that the mechanisms of leukostasis are different depending on the involvement of the monocytic lineage.

Grading of symptoms in hyperleukocytic leukaemia: a clinical model for the role of different blast types and promyelocytes in the development of leukostasis syndrome

OBJECTIVE

Patients with hyperleukocytic leukaemia were graded according to the severity of symptoms possibly caused by leukostasis to evaluate the effectiveness of therapy and to test the relative contribution of blast type and count of blasts and promyelocytes in the development of leukostasis syndrome.

METHODS

Ninety-five patients (59 male, 36 female, median age 52 yr) with hyperleukocytic leukaemia [leukocytes above 50 x 10(9)/L, 48 acute myeloid leukaemia (AML), 31 chronic myeloid leukaemia (CML), 13 acute lymphoblastic leukaemia (ALL), three chronic myelomonocytic leukaemia (CMML)] were grouped according to the presence or absence and severity of neurologic, pulmonary and other symptoms into four categories (no, possible, probable and highly probable leukostasis syndrome). Age, white blood count (WBC), haemoglobin, blast count and total of blasts plus promyelocytes of these groups were compared by Mann-Whitney U-test.

RESULTS

Patients with myeloid leukaemia (AML M1/M2, CML) which scored as highly probable leukostasis showed significantly higher WBC (P = 0.011), lower haemoglobin (P = 0.004), higher peripheral blast counts (P = 0.004) and higher total of peripheral blasts plus promyelocytes (P < 0.001) compared with the lower probability groups. In leukaemia involving the monocytic lineage (AML M4/M5, CMML) no significant differences were found in any of these factors between patients with highly probable leukostasis and the other patients.

CONCLUSIONS

Our results show that a four-stage clinical grading scale is a valuable tool for analysing hyperleukocytic patient populations and evaluate the effectiveness of therapy more precisely. We further demonstrate that the mechanisms of leukostasis are different in myeloid leukaemia as compared with leukaemia with involvement of the monocytic lineage.

Interleukin-3 receptor in acute leukemia

Recent studies indicate that abnormalities of the interleukin-3 receptor (IL-3R) are frequently observed in acute myeloid leukemias (AMLs) and may contribute to the proliferative advantage of leukemic blasts. This review analyzes the evidences indicating that the IL-3R represents one of the target molecules involved in the stimulation of proliferation of AMLs, and the overexpression of the IL-3Ralpha chain may represent one of the mechanisms contributing to the development of a highly malignant leukemic phenotype. Furthermore, there is evidence that the IL-3Ralpha is a marker of leukemic stem cells, at variance with normal stem cells that are IL-3Ralpha-. Finally, the IL-3R may represent an important target for the development of new antileukemic drugs.

Flow cytometric DNA-quantification of three-color immunophenotyped cells for subpopulation specific determination of aneuploidy and proliferation

A method is described for three-color immunophenotyping and simultaneous DNA-quantification using a flow cytometer equipped with a 488-nm argon laser and a mercury lamp (UV). The approach includes reproducible immunophenotyping comparing antigen expression before and after cell manipulation for DNA-measurement. The coefficients of variation after DNA-staining (CV=3.13 for T-cells in peripheral blood and CV=3.38 for T-cells in bone marrow) were adequate for exact DNA-analysis. For aneuploidy detection, a true internal standard was established measuring, for example, the DNA-content of T-cells in B-cell disease simultaneously with the DNA-content of the malignant cells. Using this method, aneuploidies could be unequivocally detected in 17 out of 24 patients with multiple myeloma. Furthermore, intratumor heterogeneities in DNA-content and antigen expression could be recognized, allowing an exact separation of tumor cells and normal hematopoiesis. The study also demonstrated the importance of exact immunophenotypic characterization of lymphocyte subpopulations and the determination of their specific proliferation, for example after proliferation induction in cell cultures. Future studies should address the applicability of this rather simple multiparameter approach for simultaneous immunophenotyping and DNA-measurement especially in the detection of minimal amounts of aneuploid cells after chemotherapy.